Robert Mugabe talks to the media after casting his ballot in Zimbabwe's elections. Photograph: Meng Chenguang/Rex Features

There was a time when he was welcomed to a state banquet at Buckingham Palace and knighted by the Queen. Now that Zimbabwe's president, Robert Mugabe, has all but claimed another election win, the quandary for western governments is whether the time has come to roll out the red carpet and end his international isolation.

Mugabe is seen by many respected observers as a ruthless autocrat responsible for thousands of deaths during his 33-year rule who has yet again rigged his way to victory. But despite deep misgivings about the fairness of the poll, it is conceivable that realpolitik will pressure Britain and its allies to lift the last remaining sanctions against Mugabe and his inner circle.

On Friday his Zanu-PF party summoned journalists to a rare press conference at its headquarters in the capital, Harare, predicting that a record turnout of 3.95 million voters would give it a two-thirds parliamentary majority. An exultant Patrick Chinamasa, the justice minister, suggested that the result was a historic vindication of Mugabe and defeat of the west, proof that Zanu-PF was right about everything from human rights to seizures of white-owned farms.

Throwing down the gauntlet to Britain, he said: "As far as Zanu-PF is concerned, we have never refused to talk to them. It was Blair and Brown who refused to talk to our president over a decolonisation issue to do with the land question."

Chinamasa visited the UK this year and said the Africa minister, Mark Simmonds, indicated that the government wanted to re-engage. "So I said to Mr Simmons, when you are ready, if you are able to deal with your British public opinion which you poisoned through demonisation of our president for no basis through lying that we were in violation of human rights, if you are able to think that politically you are now ready to engage us, you will find our doors open. Basically, you know where to find us."

Chinamasa denounced the travel bans and asset freezes imposed by the European Union and US, which Zanu-PF has blamed for Zimbabwe's economic crisis. "These are not from the UN, they are just from a club of white people who just don't like the fact that we are repossessing our land … The sanctions are illegal and they should be lifted yesterday, not tomorrow."

Asked whether Mugabe could one day set foot in Britain again, Chinamasa expressed hope that relations would be restored, but complained: "I was the first minister of Zanu-PF to visit London in 15 years. They lied to the public that they'd lifted sanctions against me, only to find when I got there that they were giving me a licence to buy in British shops. I never understood that British people can be so petty that I can't buy in a restaurant until I produce a licence when in fact I have been given a visa."

The Zanu-PF philosophy is fervently historical and anti-colonialist, questioning why Africa's wealth of natural resources have not alleviated poverty and insistent that land and businesses must be returned to Zimbabwean hands. Chinamasa accused western powers of funding non-government organisations in the country to the tune of $2.6bn (£1.7bn) and sponsoring pirate radio stations to effect regime change.

"We have said to Europe that they should change their mindset: we are no longer their colony," he said. "Each time they speak, they speak down on us as an enslaved people. They speak down on us as a colonised people. We want them to change that mindset. They should not continue the mindset of their grandfathers who colonised us which is what they continue doing.

"We thought that the new generation of Europeans and Americans – especially after they speak about human rights and so forth – would have a different mindset, but when you interact with them it's the same mindset that existed 500 years ago. It's like father like son, like a goat can only give birth to a kid goat, it's the same. But we are not goats, we are not animals."

He added: "We want Europe and America, white Commonwealth countries, to accept us as an equal sovereign country. If they do, they will find themselves welcome, we will receive them with open arms. That is the relationship we want to nurture between ourselves."

Mugabe banned the EU and groups including the US-based Carter Centre from monitoring the election, claiming that countries that imposed sanctions were biased in favour of the rival Movement for Democratic Change, which has called the poll "null and void". Official verdicts have therefore been left to two African observer missions - a critical test for democratic accountability on the continent.

On Friday the African Union released a preliminary report expressing concerns about the non-availability of the electoral roll and the "high incidence" of voters who were turned away at polling stations. But its head of mission, Olusegun Obasanjo, said the apparent irregularities did not constitute evidence of systematic tampering. "Yes, the election is free," Obasanjo said. "Fair? Fairly. I have never seen an election that is perfect."

Bernard Membe, head of the observer mission for the Southern African Development Community, described the election as "very free" and "very peaceful" but noted that there were some violations, and a full analysis was still under way. "The question of fairness is broad and you cannot answer it within one day," he said.

The tone of the assessments implied that both organisations would ultimately rubber-stamp the result, especially given Zanu-PF's big margin of victory. That will put western governments in a dilemma, since to directly contradict African observers would play into the hands of Zanu-PF's anti-colonialist ideology and risk causing alienation on a continent where China is making friends. Some in the EU, such as Belgium, are said to be eager for a share of Zimbabwe's diamond trade.

But one Harare-based ambassador has stuck his head above the parapet. Australia's Matthew Neuhaus sent a diplomatic cable to Canberra titled "A farcical election", and called for a rerun. "It wasn't credible, it wasn't fair," he explained later, adding that he had personally witnessed a woman being turned away and told to vote 200 miles away, manipulation of voting slips, the exclusion of young people, and a woman who found nine dead relatives on the electoral roll.

Neuhaus said he was in touch with his American and Canadian counterparts and they broadly agreed with the Zimbabwean opposition MDC's critique of the way the election was conducted. "It does make a farce of the election process and it doesn't pass the test of credibility. There's no intention to remove the remaining targeted sanctions given that the nature of this election is obvious," he said.

A spokeswoman for the US embassy in Harare said it was not yet ready to comment. The UK's ambassador, Deborah Bronnert, declined to be interviewed.

It remains to be seen whether these governments will heed their ambassadors' cables. Petina Gappah, a Zimbabwean writer and political commentator, said: "I think the process of re-engagement should continue. We live in a world where Britain does business with nasty people such as Saudi Arabia. The Foreign Office will have to accept that Zanu-PF is going to be in government for a very long time."